Students take the baccalaureate exam in rebel-held Aleppo, Syria, in August. / Council of Liberated Aleppo

by Gioia Forster and Raneem Qubatros, Special for USA TODAY

by Gioia Forster and Raneem Qubatros, Special for USA TODAY

AMMAN, Jordan - As the Syrian civil war drags into its fourth year, more than half of Syrian school-age kids are falling behind because schooling has become a casualty of the conflict.

Millions of children are not going to school; some haven't been for three years. Many schools have been destroyed in battles or taken over as combat posts.

Children have fled with their families from intense fighting to regions where schools are not fully available or too dangerous to attend. Hundreds of thousands have gone to crowded refugee camps outside the country or to foreign cities where they face barriers to assimilation.

"There are 9-year-old kids who can't read or write," said Rima Said, 29, a mother of two in the suburbs of Damascus.

Before the civil war erupted in March 2011, 4.8 million Syrian children - or 97% of primary school-age children and 67% of secondary school-age children - attended classes regularly, a recent UNICEF report found.

The country's literacy rate of 90% was on par with Turkey and Jordan and superior to Egypt and Iraq, the report said.

Today, more than 2.2 million Syrian children don't attend school. UNICEF reported that 500,000 students who have fled to refugee camps outside Syria aren't receiving education either.

The war between government and rebel forces has destroyed 4,000 school buildings, according to UNICEF. Other schools have been turned into refugee centers or worse. Human Rights Watch has reported that Syrian schools have been used as detention centers where torture has occurred.

"There are no real schools in our area," said Um Asa'ad, the widowed mother of a 15-year-old in Rastan, one of the last rebel strongholds in the northern suburbs of Homs in western Syria. "Some people do teach their kids at home, but I don't see it as good education."

Simply getting to school is often too perilous for many children. Fighters have barged into schools and harassed students and teachers, Human Rights Watch said. In regions where the fighting has been most intense, attendance rates have fallen to as low as 30%, UNICEF found.

"Our students face continuous shortages of electricity, water, housing and amenities that are supposed to be available in schools," said Mohammad Jamal Shahoud, 44, director of the Free Education Directorate in Idlib, an association of 3,000 teachers who have set up ad hoc schools throughout the war-torn country.

He said that in especially violent areas, teachers often hold classes in tents and even caves.

As children grow older, they're more likely to leave school voluntarily, said Juliette Touma, UNICEF's spokesperson on the Syria crisis.

"Children aged 12 and above are at a higher risk of leaving school and joining the labor force or fighting," she said.

Basheer, 16, who lives in Damascus, said he dropped out of school in 2012 because he didn't see much point to studying.

"I started to watch the news and see the daily killing in other provinces," he said, asking that his last name be withheld out of fear for his family's safety. "I felt humiliated and oppressed when I saw dead bodies on television."

"I left my job and started joining all protests around Damascus and tried hard not to miss a single one," he said.

Children who drop out often fall prey to exploitation, said Al-Mo'men Saed, a teacher in Damascus.

"Many kids are on the main streets now, selling things, begging for money or being exploited by people," she said. "They are working in places that don't suit their ages to make a living."

Ola Um Malek, a mother of two, fled the violence in her Damascus neighborhood and settled in another part of the capital. She has not seen her husband since police arrested him two months ago at a checkpoint in their neighborhood, and police have not responded to her pleas for an explanation.

Her two boys have been out of school for more than a year. She tried to enroll them in the regime-controlled Damascus neighborhood of Al-Midan, but the school was full because of an influx of internally displaced Syrians.

Um Malek says she is losing control of her eldest son Malek, 9.

"He has become very aggressive lately," she said. "He bullied and attacked a girl in the neighborhood and broke a cellphone belonging to a neighbor. He is so violent and neurotic all the time."

Um Asa'ad said her 15-year-old son shows similar signs of restlessness. She worries he will join the fighting rather than keep his job selling gasoline with his uncle in Rastan.

"My son spends most of his spare time sitting with rebels to get closer to them," she said. "I keep trying to stop him. It is better to work in order to learn a skill and to be able to offer us something to live from."

In the absence of other options, Um Malek said, her children spend their time mimicking what they see around them.

"They play war, some acting like they are shabiha and some are Free Syrian Army," she said, referring to a pro-regime militia and Syrian rebel forces, respectively. "They capture places and people and so on."

Shahoud said the situation worsens with every passing day as children grow older without the benefit of learning in the classroom.

Making up for lost time will be difficult, he said, as will healing the children who have experienced war up close.

"We will need more than a decade to deal with the effects of uneducated students," he said. "Students are suffering from fear, introversion and health problems such as involuntary urination â?? in ninth grade."